Consider the following statement: "Although fiscal policy clearly is useful in combating the extremes of severe recession and demand-pull inflation, it is impossible to use fiscal policy to fine-tune the economy to the full-employment, noninflationary level of real GDP and keep the economy there indefinitely."

This statement recognizes that

The statement recognizes that fiscal policy is not enough to keep an economy at full employment and with low inflation levels for a long period of type.

Explanation:

First of all, it is widely accepted by economists that society faces a short-term trade-off between inflation and employment. The reason for this is that controlling inflation in the short-term requires limiting the amount of money circulating in an economy, and less money means less saving, less investment, and thus, less employment. Hence, we can conclude that balance full employment with low inflation is extremely hard.

Secondly, fiscal policy by itself is not effective in controlling inflation. Inflation is the main goal of monteray policy, which is set by the central bank (in the United States, the Federal Reserve system), and uses a set of tools to achieve the aim of low inflation.